1. Field of the Invention
The present invention relates to parallel plate electrostatic actuator using thin films, and more specifically, to an electrostatic actuator improved in the linear movability toward a moving direction.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 09-233858) discloses an electrostatic actuator improved in controllability by reducing fluctuations in thrust due to the positional relationship between a mover and a stator by arranging the mover and the stator with a specified inclination (skew) provided, as illustrated in FIGS. 5 and 6 in this patent document.
Furthermore, Japanese Unexamined Patent Application Publication No. 2001-162599 discloses a rotational actuator having a mover and a stator with electrodes arranged in a zigzag manner.
Generally, in the electrostatic actuator, it is required not only that the mover can move, but also that the mover can move straight toward a moving direction with respect to the stator. In other words, the electrostatic actuator is required to have a high linear movability during moving.
However, due to a slight unevenness of an opposing gap between the stator and the mover, a stronger force operates in the narrower gap portion, while a weaker force operates in the wider gap portion. On the other hand, if the mover receives some external force, a force that displaces the mover toward its widthwise direction acts on the mover. Because such forces operate in an oblique direction relative to a traveling direction, there occurs a possibility that the mover may assume an inclined posture, resulting in an inoperative state.
Therefore, there is a need to install guide means for preventing the mover from the inclining. However, this causes problems such as a loss of thrust owing to a sliding resistance generated by the guide means, and the complication of the structure and the increase in assembly procedures due to the installation of the guide means.
In regard to this point, the actuator disclosed in the Japanese Unexamined Patent Application Publication No. 09-233858 sets forth the reduction in fluctuations of thrust, but does not refer to the linear movability during moving at all.
On the other hand, since the actuator disclosed in Japanese Unexamined Patent Application Publication No. 2001-162599 is a rotational actuator, the linear movability during moving constitutes no problem. Therefore, in this patent document, although a way of obtaining a maximum rotational driving force by arranging electrodes in a zigzag manner is described, a technique for enhancing the linear movability is not referred to at all.